Drug Targets Link between Glioblastoma Stem Cells and Circadian Clock Proteins

A Keck School of Medicine of USC-led research team has demonstrated that circadian clock proteins, which help to coordinate changes in the body’s functions over the course of a day, may play a key role in glioblastoma growth and proliferation after current standard treatments. The discovery has led to the identification of a small molecule drug, known as SHP656, which can target the clock proteins and may prove effective for treating glioblastoma. The team’s reported study demonstrated that the active isomer of the drug, designated SHP1703, inhibited the growth of patient-derived glioblastoma stem cells (GSCs) in culture.

“This is a potent molecule that’s very exciting to us in terms of its potential for deployment against glioblastoma,” said Steve Kay, PhD, University and Provost Professor of neurology, biomedical engineering and biological sciences at the Keck School of Medicine of USC and director of the USC Michelson Center for Convergent Bioscience. “We’re now starting to march down the path of clinical drug development—turning this from a science story into a translational one.” Kay, who also codirects the Rosalie and Harold Rae Brown Center for Cancer Drug Development at the USC Norris Comprehensive Cancer Center, is senior author of the team’s published study in PNAS, which is titled “CRY2 isoform selectivity of a circadian clock modulator with antiglioblastoma efficacy.”

As the most common form of brain cancer in adults, glioblastoma is an aggressive disease. Patients survive an average of just 15 months once they are diagnosed. Despite more than two decades of research on the causes and treatments of glioblastoma, that prognosis has hardly improved.

The first symptoms of glioblastoma can include blurred vision, headaches and nausea, and even seizures and personality changes. Patients typically undergo a brain scan, which identifies the tumor, then receive a combination of surgery, radiation and chemotherapy treatment. While most tumors shrink substantially after the initial treatment, few patients experience sustained remission. “In the vast majority of patients, the cancer returns. And when it returns, it’s resistant to chemotherapy and radiation,” Kay said.

Researchers believe that the cancer returns because a small number of cancer stem cells are left behind after surgery, chemotherapy and radiation. These stem cells can multiply and spread very quickly. Research by Kay’s team helps to explain why. He and Jeremy N. Rich, MD, at the University of Pittsburgh, found that cancer stem cells hijack the body’s circadian clock machinery, allowing them to spread more quickly and resist the effects of chemotherapy and radiation treatment. The circadian clock encompasses a number of what the authors described as “ … a cell-autonomous network of molecular interactions that enables endogenous regulation of daily physiological rhythms, while allowing for inputs from environmental cues.” The mammalian cryptochrome isoforms CRY1 and CRY2 are core circadian clock regulators, the team continued. “CRYs are core components of the circadian clock, and CRY modulation has been shown to regulate metabolic homeostasis in animal disease models.”

Dysfunction in the circadian clock has also been associated with cancer and metabolic diseases,” the investigators continued. Proper functioning of the circadian clock is important for physiological homeostasis, and its dysfunction has been associated with a variety of diseases. “For example, mutations in CRY1 and CRY2 genes are known to induce sleep phase disorders in humans, and the genetic loss of Cry1 and Cry2 in mice results in glucose intolerance, while Cry1 overexpression in the liver lowers blood glucose levels by inhibiting glucagon response.”

Having found that the cancer stem cells might hijack circadian clock mechanisms, Kay and colleagues then created and tested thousands of molecules capable of binding to—and potentially neutralizing—the rogue circadian clock proteins inside cancer stem cells. To do this Kay assembled a collaborative group that unites academics with expertise in glioblastoma, circadian clock biology and biological chemistry with Synchronicity Pharma, a biotechnology startup that Kay co-founded.

For their newly reported studies the collaborators used several advanced techniques, including artificial intelligence, to determine which molecule was best suited to fight glioblastoma. The team’s AI algorithms modelled how each new molecule would bind to the clock proteins, searching for the perfect “lock-and-key” fit.

Their newly reported work highlighted one particularly promising molecule, known as SHP656, which is an orally available derivative of a molecule, KL001, which was the first synthetic small molecule compound found to target CRY proteins. “KL001 was the first identified small-molecule CRY modulator that activates both CRY1 and CRY2,” the team explained.

The next step was to test the effectiveness of SHP656 against actual cancer cells. Using glioblastoma stem cells collected from patients, the researchers showed that the drug reduced the growth of cancer stem cells, but did not harm the body’s normal stem cells. “… we have determined that SHP656 selectively binds to CRY2.” The data show that CRY2 can regulate GSC growth and survival, and demonstrate the potential of CRY2-selective activation in the treatment of glioblastoma,” the authors reported. “Our data highlight the importance of determining the isoform selectivity of compounds, as well as the active isomer, to facilitate the understanding of individual roles of CRY isoforms in disease, and to increase the potency and efficacy of compounds.”

“We’re seeing that the molecule acts differently on healthy brain cells versus tumor cells,” Kay said. “This was a real leap forward in our understanding of how we can develop drugs that target clock proteins.” The authors further pointed out, “Further investigation of in vivo properties and efficacy of SHP1703 will provide a rationale for the use of CRY-targeting compounds as a therapy paradigm for glioblastoma treatment.”

Synchronicity Pharma has now begun Phase I clinical trials for this class of new molecules. So far, the molecule appears to be safe in healthy volunteers. The hope is to begin Phase II trials in glioblastoma patients within two to three years.

In addition to its potential for treating glioblastoma, SHP656 and other molecules that target clock proteins hold promise for treating other types of cancer. Kay and his colleagues are also studying their utility in colorectal cancer, liver cancer, and acute myeloid leukemia. “This study shows that when you bring together the right kind of collaborative, academic researchers can be leaders in the discovery of cancer drugs,” he said.

The authors concluded, “Our results suggest a direct role of CRY2 in glioblastoma antitumorigenesis and provide a rationale for the selective modulation of CRY isoforms in the therapeutic treatment of glioblastoma and other circadian clock-related diseases … Future experiments utilizing CRY1-selective compounds could help elucidate overlapping and distinct roles of CRY isoforms in glioblastoma and other types of cancer as well as circadian clock–related diseases.”